1. Field of the Invention
This invention relates to an improvement on a clutch facing of a clutch disk, used in an automobile, for connecting and disconnecting the power transmission, and particularly relates to a resin mold clutch facing having lower specific gravity, high strength, and good friction and anti-wear properties at a high temperature.
2. Discussion of the Background
An automobile employs a clutch facing as one of the components of a clutch disk for connecting and disconnecting the power transmission between the engine and the gearbox.
The followings have been known as the clutch facing: a woven clutch facing, a semi-mold clutch facing, and a resin mold clutch facing.
The woven clutch facing is formed by winding a string shaped fiber, which has been impregnated with a resin in advance, in a spiral shape, and thereafter by molding the string shaped fiber into a desired shape.
The semi-mold clutch facing is formed by winding a string shaped fiber, which has been impregnated with a resin and a rubber, in a spiral shape, and thereafter by molding the string shaped fiber into a desired shape.
The resin mold clutch facing is formed by dry-mixing a short fiber as a matrix, a resin and additives, and thereafter molding the mixture into a desired shape. Hereinafter, the short fiber means a discontinuous fiber or filament of an interrupted length.
However, as to the woven clutch facing and the semi-mold clutch facing, the additives should be impregnated into the string shaped fiber, and the types and the amounts of the additives are limited. As to the semi-mold clutch facing, the additives have been mixed with the rubber and impregnated into the string shaped fiber, thereby increasing the contents of the additives and improving the anti-wear property. However, no further improvement on the performance can be expected because the current mixing amounts of the additives have nearly reached the limitation.
On the other hand, as to the resin mold clutch facing, it is easy to add the additives to the mixture and to improve the friction property because the components of the mixtures are dry-mixed and molded. Therefore, the improvements on the resin mold clutch facing is the current trend in the field of the clutch facing development.
The resin mold clutch facing has a uniform friction property because it has a uniform composition in any part thereof. On the contrary, the resin mold clutch facing has a problem on the shear strength. Namely, the resin mold has low shear strength because the fibers thereof do not have a uniform orientation. Accordingly, the resin mold clutch facing has a problem on the burst strength, namely the resin mold clutch facing has low revolution per minute (hereinafter referred to as rpm) at burst. Here, the rpm at burst means the rpm at which a clutch facing bursts. That is, the clutch facing is rotated at high speeds while gradually increasing the rpm until the clutch facing bursts. Therefore, the clutch facing is judged to be superior in the strength when it shows higher rpm at burst.
U.S. Pat. No. 4,244,944 discloses a laminated aramid fiber friction member having two-layer structure, comprising a base member and a backup member, similarly to the present invention. However, the laminated friction member has following two problems.
a) Coupling strength is weakened at a high temperature since the member contains rubber component.
b) The volume percentage between the glass fiber and the polyamind fiber in the base member is different from that in the backup member, in other words, the volume percentage of glass is larger than that of polyamid in the base member, however, the volume percentage of glass is smaller than that of polyamid in the backup member. Therefore, warpage may be occured owing to the difference of their coefficient expansion, during the operation.
We, the inventors of the present invention, had proposed a resin mold clutch facing in Japanese Unexamined Patent Publication (KOKAI) No. 203936/1988 to solve the above-mentioned problems.
The resin mold clutch facing set forth in the publication is integrally heat molded out of a resin mold base member forming a friction face, and a backup member. The resin mold base member consists essentially of a matrix composed of a glass fiber and an aromatic polyamide fiber, an inorganic filler, a solid lubricant, and a resin binder. The backup member consists essentially of a matrix composed of a glass strand or yarn and at least one strand or yarn selected from a group consisting of a rayon strand or yarn and an aromatic polyamide strand or yarn, and a binder adhered to the matrix, and is shaped in an spirally wound configuration. Hereinafter, the strand or yarn means a bundle of continuous fibers or filaments of an uninterrupted length.
The weight of the resin mold clutch facing has been reduced and the strength thereof has been increased because a certain amount of the glass fiber has been substituted by the aromatic polyamide fiber having low specific gravity and high strength. Moreover, the strength of the resin mold clutch facing has been further increased because the backup member is shaped in a spirally wound configuration.
Further, because the glass fiber constituting the matrix of the resin mold base member has a softening point of from 700.degree. to 850.degree. C., the glass fiber softens at about 700.degree. C. or more and forms a heat resistance protective coat on the friction face of the resin mold base member. On the other hand, however, the strength of the glass fiber decreases remarkably when the temperature of the operating resin mold clutch facing reaches the softening point. Hence, the resin mold clutch facing set forth wears, and is not so excellent in the anti-wear property.